Experimental Physics and
Industrial Control System

Hi Pavel,

 

That may depend on which architecture you are talking about.

 

On Linux it is definitely possible to link a static library (.a) into the shared support library (.so).

 

Here is an example.   My Makefile contains this line:

 

LIB_LIBS += PvAPI

 

This is libPvAPI.a, which is a static vendor library:

-r--r--r-- 1 epics epics 2053154 Aug  6 09:34 libPvAPI.a

 

When I link my shared support library this is what I get:

-r-xr-xr-x 1 epics epics 1250968 Sep 22 11:08 libprosilica.so

 

Note that it is about 1.25 MB.

 

I then comment out the LIB_LIBS line in my Makefile and build again.  This is what I get:

 

-r-xr-xr-x 1 epics epics  115746 Sep 22 11:09 libprosilica.so

 

So now it is only 0.12 MB because libPvAPI.a is not linked into the shareable library.

 

Interestingly you will note that Linux does not give an error when the LIB_LIBS line is commented out.  Linux is happy to build a shareable library with unresolved references. In this case libPvAPI.a would need to be linked into the final application, but it does not need to be linked into the shareable library.

 

This is NOT true on Windows, either Visual Studio or Cygwin.  In that case when building the shareable library (.dll) all references must be resolved, so the LIB_LIBS link is required.

 

I believe that Windows will also allow linking a static library into a DLL, but I could not quickly find an example to prove it.

 

Mark